1. Field of the Invention
This invention is directed to audio amplifier circuitry, and in particular to such circuitry for simulating two-channel audio amplifiers, i.e. audio amplifiers having two alternate channels for signal amplification, but using only a single amplifying channel for providing either selective distortion or non-distorted ("clean" audio output) modes of amplification of audio signals.
2. Background of the Invention
This invention is related to the subject matter disclosed in U.S. Pat. No. 4,405,832, "CIRCUIT FOR DISTORTING AN AUDIO SIGNAL", issued in the name of Jack C. Sondermeyer (a co-inventor of the subject application) on Sept. 20, 1983. The disclosure of that U.S. patent is incorporated herein by reference.
U.S. Pat. No. 4,405,832 discloses distortion generating circuitry including high gain amplification with a variable, controlled feedback network for varying the gain and frequency response thereof. The specific distortion generation is disclosed as a pair of oppositely poled, anti-parallelly-connected diodes, functioning to clip the output signal of an amplifier stage in the single amplifying channel. The feedback network includes a first control means for controlling gain and frequency response of the amplifier associated with the feedback network; and a second control means for mixing the output of the amplifier with the output of the clipping or distortion circuit in variable proportions. The first and second controls are preferably ganged, thereby enabling "tracking" between the amount of gain and the degree of clipping simultaneously with frequency response modification of the amplified output signal to enhance the harmonics of the input signal to the amplifying channel circuitry.
The amplifying circuitry of the aforementioned U.S. patent describes independently operable control switches for switching between normal amplification of audio input signals, whereby a "clean" sound is output, or distortion amplification of the audio input signals, whereby the amplified signals are distorted to enhance the sound of the audio output.
The ganged normal/distortion amplification control of the aforementioned U.S. patent has the disadvantage that it provides relatively broad band gain, as the gain of a pre-amplifier stage is effectively electrically connected constantly regardless of the mode of operation, i.e., normal or distorted output.